Unverified Commit fc94368b authored by Qiliang Yuan's avatar Qiliang Yuan Committed by Christian Brauner
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fs/file: optimize close_range() complexity from O(N) to O(Sparse) 



In close_range(), the kernel traditionally performs a linear scan over the
[fd, max_fd] range, resulting in O(N) complexity where N is the range size.
For processes with sparse FD tables, this is inefficient as it checks many
unallocated slots.

This patch optimizes __range_close() by using find_next_bit() on the
open_fds bitmap to skip holes. This shifts the algorithmic complexity from
O(Range Size) to O(Active FDs), providing a significant performance boost
for large-range close operations on sparse file descriptor tables.

Signed-off-by: default avatarQiliang Yuan <realwujing@gmail.com>
Signed-off-by: default avatarQiliang Yuan <yuanql9@chinatelecom.cn>
Link: https://patch.msgid.link/20260123081221.659125-1-realwujing@gmail.com


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 6cbfdf89

fs/file.c

+8 −2
Original line number Diff line number Diff line
@@ -777,23 +777,29 @@ static inline void __range_close(struct files_struct *files, unsigned int fd, 
				 unsigned int max_fd)

{

	struct file *file;

	struct fdtable *fdt;

	unsigned n;



	spin_lock(&files->file_lock);

	n = last_fd(files_fdtable(files));

	fdt = files_fdtable(files);

	n = last_fd(fdt);

	max_fd = min(max_fd, n);



	for (; fd <= max_fd; fd++) {

	for (fd = find_next_bit(fdt->open_fds, max_fd + 1, fd);

	     fd <= max_fd;

	     fd = find_next_bit(fdt->open_fds, max_fd + 1, fd + 1)) {

		file = file_close_fd_locked(files, fd);

		if (file) {

			spin_unlock(&files->file_lock);

			filp_close(file, files);

			cond_resched();

			spin_lock(&files->file_lock);

			fdt = files_fdtable(files);

		} else if (need_resched()) {

			spin_unlock(&files->file_lock);

			cond_resched();

			spin_lock(&files->file_lock);

			fdt = files_fdtable(files);

		}

	}

	spin_unlock(&files->file_lock);